This application claims the benefit of German patent application DE P 10104419.4 filed Feb. 1, 2001, herein incorporated by reference.
1. Field of the Invention
The invention is relative to a device for the radial attitude control of a rapidly rotating rotor, especially a spinning rotor, supported in a contactless manner.
2. Background of the Invention
Contactless, passive support bearings or contactless, active supports with regulators for attitude stabilization or damping of oscillations are known in a great variety of embodiments.
For example, German Patent Publication DE 33 23 648 A1 shows a magnetic support comprising an actuating mechanism with electromagnetic coils. The magnetic support comprises two bearing parts offset relative to one another along the direction of the axis of rotation of a rotor. Translatory deviations of the instantaneous position of the axis of rotation from an ideal position are to be determined for two directions perpendicular to one another and to the axis of rotation of the rotor and stabilized by the controlling of magnetic forces. In addition, tilting movements of the rotor about axes of rotation parallel to the two directions perpendicular to the axis of rotation are determined and a restoring moment generated about these axes, and switching means are further provided for damping the nutation frequency. The nutation of the rotor is damped thereby by cross-coupling branches. Since all attitudinal deviations are stabilized, there is a constant readjusting in the case of high rotor speeds and the actuating mechanism is highly controlled. This is disadvantageous as concerns the consumption of energy and the load on the control elements and causes limitation phenomena in the control of the actuating mechanism, such as, for example, in the amplifiers. In particular, an elevation of amplitude in the so-called D-component in regulators (for example, in PD controllers or regulators) results at high frequencies and at high speeds and thereby results in high amplitude values of the control voltage. As a consequence, the power requirement of such a control is high. When the rotor speed is accelerated, increased power is required only for a brief time, for example, for fractions of a second as the speed passes through a resonance frequency of the support system. High power is constantly necessary in such attitude controls at the high operating speeds of rapidly rotating rotors, such as, e.g., in the case of spinning rotors.
In order to achieve a certain quietness and to be able to operate with less power, it is known that the rotor can be allowed to rotate not about its geometric axis but rather about its axis through the center of gravity or about the axis of inertia. For example, German Patent Publication DE 26 58 668 A1 discloses a magnetic support for a rotor in which the disturbing influences stemming in particular from imbalances and dependent on the rotor speed are reduced by means of a suppression filter. To this end, the control circuit of the magnetic support comprises a filter device interposed between the sensor device and the control circuit for the signals supplied from the sensor device. The filter device is designed as a suppression device whose frequency is adjusted according to the speed of the rotor. The suppression filter filters out disturbances of the rotor attitude that occur periodically with the rotational frequency and that would bring about a constant readjusting of the rotor into the central attitude. To this end, adding circuits and a negative feedback circuit are used. However, great complexity is necessary for the described circuits, which results in a relative great susceptibility to interference in the entire circuit. Moreover, such filter circuits cause significant phase rotations and/or phase errors that are generally recognized as disadvantageous. These phase rotations or errors can amount to more than 90 degrees and can endanger the stability of the control circuit or else which must themselves be compensated for in an expensive manner. Due to the carried-out adjustment of the effect of the suppression filter to a certain rotational speed of the rotor the desired effect does not occur at rotary frequencies deviating from this adjustment.
German Patent Publication DE 31 20 691 A1 describes a magnetic support in which deviations from the geometry of the rotor are detected by a sensor device and stored in a data storage along with the corresponding particular angular position at the rotary motion of the rotor. The detection takes place in a rotor-specific manner and is carried out before the particular rotor is put in operation. The stored values remain preserved for the entire operating time of the rotor. The disturbance signals generated by the sensor device and those deriving from errors of geometry are superposed and thus compensated by means of a correction signal. Unfortunately, the use of such a device, especially in spinning rotors of a rotor spinning machine, has disadvantages. Spinning rotors are subject to wear that can necessitate the replacement of the particular spinning rotor. If necessary, spinning rotors are also replaced during a batch change as a function of the fibrous material or yarn used. Thus, the replacement of spinning rotors that is unavoidably repeated when using spinning rotors requires significant expense on account of repeated detection operations. Also, a rather large computer capacity must constantly be available in order to store the amounts of data and to continuously process them. Further, imbalances which are not traceable to detectable errors of geometry, such as imbalances due to inhomogeneity of the rotor material or due to trash that can adhere and collect in the area of the rotor groove of spinning rotors, are not compensated in the device described in German Patent Publication DE 31 20 691 A1.
The present invention seeks to address the problem of improving the attitude control of rotors which are supported in a contactless manner.
The invention addresses this problem by providing a sensor device for the continuous generation of rotor attitude signals and a control device for processing the rotor attitude signals. The control device includes a controller that outputs a rotary-frequency-dependent output resultant signal or correcting variable, generated from the rotor attitude signals, for controlling the actuating device. The resultant signal follows the rotary-frequent waveform of the controller output signal at frequencies below the resonance frequencies of the contactless support, while above these resonance frequencies the resultant signal increasingly follows the rotary-frequent waveform of the controller output signal only in the area of at least one of the two extreme values (i.e., the minimum and maximum values) of the waveform, whereby the amplitude of the resultant signal is distinctly smaller than the amplitude of the rotary-frequency-dependent controller output signal. Further, the resultant signal of the rotary-frequency-dependent oscillation maps superposed oscillations of the controller output signal that are low-frequency in comparison to it in a practically unchanged manner.
Such a control device permits, upon the occurrence of rather high oscillatory frequencies, the lowering of the oscillation amplitudes of the oscillation dependent on the rotary frequency with small phase errors at the same time as regards the relatively low resonance frequencies and therewith permits an advantageous reduction of the power consumption of the attitude control as well as increased quietness of the rotor without customary suppression filters and without the above-mentioned disadvantages of the state of the art. The small phase errors that occur thereby do not endanger the stability of the control and are tolerable. On the other hand, the phase rotation that can be produced by customary deep-pass filters is significantly greater.
The reduction of the amplitude of the rotary-frequency-dependent oscillation of the resultant signal relative to the amplitude of the rotary-frequency-dependent oscillation of the controller output signal is preferably brought about by limiting the rise of the curve of the resultant signal to a maximum amount outside of the areas in which the resultant signal follows the waveform of the controller output signal. The concept xe2x80x9cfollowxe2x80x9d used here also includes the instance in which there is only a slight difference between the resultant signal and the waveform of the controller output signal. The limitation of the rise applies not just to the area in which the rise of the controller output signal is positive, but also the area in which the rise of the oscillation of the controller output signal is negative (that is, if the curve falls). In the latter case, the rise of the curve and the slope of the resulting waveform are likewise limited to the maximum amount. The maximum amount can therefore also be considered as an absolute amount. As long as the rise of the controller output signal is below the limitation, the resultant signal follows the controller output signal and the control corresponds completely to the control algorithm. In contrast thereto, in the case of higher-frequency, rotary-frequency-dependent oscillations of the control output signal in which the waveform of the controller output signal sharply rises or falls and the rise exceeds the limitation, a reduction in the amplitude occurs, in accordance with the invention, in the rotary-frequency-dependent oscillations of the resultant signal used to generate the actuator control signal for the actuating device. For example, the magnitude of a voltage or of a current can be used as signal magnitude or as a correcting variable. The distinct reduction of signal components with high frequency and high amplitude, such as, for example, the rotary-frequency-dependent oscillation components of the controller output signal in the resultant signal, opens the possibility of an expanded ability to control low-frequency disturbing influences, such as, for example, the nutation of a rotor, without having to fear an overloading, of, for example, the actuating elements. The amplitude- and phase error produced in the amplitude reduction of the rotary-frequency-dependent oscillation components remains so slight or negligible that no instability of the control can occur. The avoidance of an overload as well as the extant stability of the control increase the operational safety. The apparatus of the present invention can be flexibly used as regards the rotor speeds, and is not subject to any limitation in as far as the presence or maintenance of a predetermined speed is concerned.
The advantageous effect of the invention can be achieved in a relatively simple manner and with low expense if the area in which the limitation of the rise of the curve of the resultant signal is effective over a maximum amount begins at the extreme value and ends when the value of the controller output signal attains again the instantaneous value of the resultant signal.
In an advantageous embodiment the control device is set in such a manner that the width of the particular area in which the resultant signal follows the waveform of the controller output signal is determined as a function of the rotary frequency and outside of these areas the rise of the curve of the resultant signal is preferably zero.
In the case of relatively low-frequency oscillations, such as in the case of support resonance frequencies, the area in which the resultant signal follows the waveform of the controller output signal may extend over the entire waveform. In the case of frequencies so far above the support resonance frequencies that their damping cannot be adversely impacted, the other area, in which the limitation of the rise takes effect and the rise is therewith constant in this other area, also participates in the waveform of the resultant signal. As the rotary frequency rises, the amount of the other area is increased to the extent to which the amount of the first area drops. As a result of the fact that the resultant signal still follows the controller output signal in a periodically reoccurring fashion in at least one area, the resultant signal remains phase-locked to the particular rotary frequency. The phase is synchronized and a drifting off avoided.
In another preferred embodiment of the present invention, a processor may be utilized to determine the width and the position of the respective first area, in which the resultant signal follows the waveform of the controller output signal, and of the other area, in which the rise is limited. The same effect can be achieved at a low cost without the necessity of making computer capacity available by means of a suitable circuit.
In another preferred embodiment of the present invention, the direct current component of the signal can be decoupled in a simple manner with a capacitor connected in after the control device. The passage of the nutation frequency takes place without appreciable phase error and without appreciable phase shift. The nutation of the rotor, especially that of a spinning rotor, can thus be effectively damped.
The control device is preferably set so that the rotary frequency at which the waveform of the resultant signal follows the waveform of the controller output signal only in the area of one of the two extreme values is at least twice as high as the decisive resonance frequency of the contactless support. High speed frequencies and/or oscillation frequencies occur, if, for example, the rotor is a spinning rotor rotating at the operating speed. Low-frequency resonance oscillations of the support system operating in a contactless manner that are to be damped remain preserved practically unaffected, and these oscillations can be effectively stabilized or damped by the signal used as the correcting variable.
The control device is preferably set up for forming a new signal as the arithmetic average of two resultant signals. One resultant signal follows the waveform of the controller output signal only in the area of one of the two extreme values and the other resultant signal follows it only in the area of the other of the two extreme values, and the new signal formed from the arithmetic average is advantageously output as the actuating control signal to the actuating device. In this manner an improved smoothing of the signal used as the correcting variable can be achieved with a further resulting lowering of the power requirement of the rotor support control.
A quasi-symmetric circuit design having two branches, each of which includes at least one diode, a capacitor whose capacitance determines the maximum amount of the rise for the area in which the limitation is effective, a constant current source and a resistor, requires no great expenditure for construction or any computer capacities. A-D converters or D-A converters are not necessary with this circuit because the signal processing can take place in a totally analog manner. The range of the area in which the resultant signal follows the controller output signal is generated automatically as a function of the rotary frequency.
The amplitude-lowering effect of the device of the invention may be improved by using resistors in the circuit such that the currents flowing in the respective resistors are distinctly smaller than the currents flowing in its associated constant current source
If the contactless support is an active magnetic support, available actuating elements can be used.
The effect produced by the lowering of the amplitudes corresponds to a so-called imbalance suppression. If the rotor rotates on its axis of inertia or its axis of gravitation, no continuous readjusting with high controlling of the actuating elements takes place. The power required for attitude control is relatively low. The device of the invention constitutes a simple, very economical and energy-saving but very effective means for attitude control and for active damping when passing through the support resonance frequencies and particularly in the nutation of rotors supported in a contactless manner. The device of the invention can achieve, in addition to the low consumption of energy, an expanded ability to control and greater operational safety in radial support controls of a rapidly rotating rotor supported in a contactless manner, especially of a spinning rotor.
Further details of the invention will be understood from the following description of an exemplary embodiment with reference to the accompanying drawings.